Freeness tester for pulp



may 3, 1927. 3352mm W. B. CAMPBELL.

FREENESS TESTER FOR PULP Filed June 21. 1926 INVENTOR wlLuAnBoYamMPBELL I [VG ATTORNE Patented May 3, 1927.

, 1,627,010 NMED STATE-S PP ATE NT Q F F I CE.

'WILLIAM "BO'YD CAMPBELL, CF'MONTREALfQUEBEC, CANADA.-

FBEENESS TESTER-FOR PULP.

Thisinvention ielates to'new and useful improvements in the method of and apparatus for measuring the resistance offered to theflow of water through a bed of granular orifibrous material, and the object of the invention is to'provide a simple and efficient means for measuring the resistance aforementioned, without the necessityfor timing the flow of water or of measuring the temperature .at which the test is made.

'The device particularly adapted for testing paper pulp during the course of man- 'ufacture,and is known in the art as a freeness tester.

From experiments on the mechanics of freenesstesters of the type at present in use, it is evident that the freeness measured is really an indirect measure ofthe resistance oflered by pulp to the flow of water through it,ithe pulp being in the condition in which it is found when it isdeposited on a screen from a dilute suspension. The figures. given by any of thetesters at present in use, do not bear a direct relationship to this resistance since it involves severaltfactors inherent in the particular tester used.

"Oneofthe outstanding advantages of the freenesstester of the type at present in use, is that there is no necessity. for making measurement of time, but it has several disadvantages, one of which isits sensitivity to the temperature at which the determination' is made. Another disadvantage is the comparatively large effect of small variations'inthe-screenplate of the drainage chamber. A still further disadvantage is the variation in the freeness found if the time taken between starting the drainage and pouring the stock into the chamber is varied.

In my invention the apparatus used avoids the aforementioned disadvantages, while it retains the advantage of avoiding the necessity of timing the flow.

In the drawing which illustrates in diagrammatic form an apparatus suitable for testing the freeness of pulp by my improved method, 1 designates a constant level flow box, supplied by a stream of water through the side connection 2. This water flows in part through a short length of capillary tubing 3, and the overflow goes to waste through an overflow pipe 4. The head of water being constant, the flow of Water through the capillary tube is proportional to the fluidity of the water. The lower part Application filed June 21,

through the capillary tube.

pulp sample under test, is. placed withinthe larger portion '6 of the'tube and acrossthe opemngthereof. Just below the-point 9 where the tube broadens out, a baffle 10 is placed to break upthe stream line of' flow through the narrow portion of the tube 5,

and allow it to distribute over thelarger area of the screen 7.

the tube't"), said upper end being funnelshaped to facilitate this operation. As the dilute pulp flows downthroughthe tube,

the water drainsfrom it through the screen plate and a sheet or. mat of pulp is deposited on theplate. Thepulp is thus deposited mthe same manner .as it is on a paperma chine wire. Water is, meanwhile flowing in at a constant rate through capillary tube and this water must pass through thepulp accumulated on the screen plate before passmg out. 'lVhen'the pulp is allin themat, a stable equilibrium will be established, so that there will be a head of water in the tube 5 just sufficient to cause-as much-water to flow out. through thelpulp matas'coi'nes in At any one temperature the viscosity ofthe water is constant and there will therefor be a definite flow of water through the pulp. The pulp is spread over a definite area so that the resistance it offers to the definite flow is proportional to its slowness and its amount. The amount of the pulp is known from other determinations of consistency. The resistance offered is read off from the graduated tube at equilibrium. The flow is known from previous calibration of the instrument. From these various factors the slowness of the pulp can be calculated in centimeter, gram, second units as offering a resistance of so many centimeters of water head per gram of pulp per square centimeter to a flow of one cubic centimeter per second. If it is desired to use freeness as a measure rather than slowness the reciprocal of the foregoing may be taken.

It is obvious that the test avoids the necessity of time measurements. How the disadvantages mentioned above are avoided may require some explanation. In the testers at present in use the temperature affects the test since itafliects the viscosity of the water on which the rate of flow through the pulp depends. Viscosity has practically no effect on turbulent flow or hydraulic flow, but it has a large efl ect on stream line flow, such as'takes place through the pulp mat. In this tester herein disclosed the same effect will take place i. e. the flow through the pulp will be more rapid as the viscosity is decreased through rise in temperature but so far as the resistance reading is concerned this etlect is exactly balanced by the similar eltect on the flow through the capillary tube through which the flow is of the stream line type. The effect of variations in the screen plate is eliminated for all practical purposes since its resistance is an extremely small part of the total resistance. This is not thecase in the usual type of tester at present in use, particularly at the start of the flow which is the most important time. Since all the pulp on the screen plate, the time of settling ceases to have any influence.

The amount of flow can be set for any capillary used by regulating the head under which it operated, so that even it various sizes of capillaries are used, they will all give the same result if the heads under which they operate are appropriately chosen.

In addition to avoiding these various difiiculties, Found in the usual type of tester, the tester herein disclosed has the advantage of giving its results in absolute terms such as can be used in connection with sheet formation on the wire of a paper making machine. Very little diliiculty would be encountered in making this device a recording instrument provided a reliable consistency regulator were available.

Having thus described my invention, what I claim is 1. An apparatus for measuring the resistance offered to a flow of water through a porous mat of material, comprising a graduated tube closed at its lower end by a screen plate to support the mat of material, and a device for feeding water to the tube at a fixed rate of [low sutiicient to cause the water to rise in the tube so as to register with the graduations thereon.

An apparatus for measuring the resistance ott'cred to a flow of water through a porous mat of material, comprising a graduated tube expanded at its lower end, a screen plate supported in said end and upon which the material under test rests, and a constant level feed tank having a capillary tube depending from its lower end, the tube being above the graduated tube and adapted to discharge thereinto.

3. An apparatus for measuring the resistance oliered to a flow of water through a mat of pulp, comprising a graduated tube expanded at its lower end, a screen plate secured to said end and covering the openiug therefrom, means within the end above the screen. plate to distribute pulp passing through the tube, evenly over the screen plate, a constant level water feed supply chamber luiving a capillary tube depending therefrom, and positioned over the graduated tube so as to discharge thereinto.

4. A method of measuring the resistance otl'ered by a mat of pulp to the passage of water therethrough, consisting of pouring a sample of diluted pulp through a vertical tube the lower end of which is closed by a screen plate over which the pulp becomes distributed, passing water through the tube and the distributed pulp at a fixed rate o't .tlow such that the water level will rise into the tube and finally reach a constant level therein, and measuring the height of said constant level.

in witness whereof I have hereunto set my hand.

W. BOYD CAMPBELL.

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